1. Field of the Invention
The present invention relates to a method for making a strontium titanate based Grain-Boundary Barrier Layer Capacitor (GBBLC). More particularly, it relates to a method for making strontium titanate based GBBLC with improved dielectric properties by introducing an additional heat-treatment step during the fabrication process.
2. Description of the Prior Art
There have been efforts to develop capacitors to meet high capacitance and small size needed for low voltage circuitry. Strontium titanate based GBBLC has a high dielectric constant because the thin grain boundary barrier layers formed between semiconductive grains function as dielectric layers. Thus strontium titanate based GBBLC is a passive component widely applied to electronic circuits. Strontium titanate based GBBLC is prepared by sintering a powder mixture of strontium titanate and n-type dopants, such as Nb.sub.2 O.sub.5 and La.sub.2 O.sub.3 [See, M. Fujimoto and W. D. Kingery, J. Am. Ceram. Soc., 68[4] 169-73 (1985)] in a reducing atmosphere, and coating the sintered bodies with powdery metal oxides with low melting points, such as PbO, Bi.sub.2 O.sub.3, and CuO, and then annealing the coated bodies in an oxidizing atmosphere to form a thin insulating layer between SrTiO.sub.3 grains [See, Franken et al., J. Am. Ceram. Soc., 64[12], 687(1981)]. This fabrication process leads to a very high effective dielectric constant. The electronic properties of strontium titanate based GBBLC thus strongly depend on the sintering and annealing conditions. Previous methods of making strontium titanate based GBBLC consists of sintering power compacts in a reducing atmosphere and infiltrating an oxide liquid glass into the sintered compacts in air.